#include <iostream>
#include <vector>
#include <string>
#include <unordered_map>
using namespace std;

class Solution {
public:
    int peakIndexInMountainArray(vector<int>& arr) {
        int left = 0, right = arr.size() - 1;
        while (left < right)
        {
            int mid = (left + right) / 2;
            if (arr[mid] < arr[mid + 1])
                left = mid + 1;
            else
                right = mid;
        }
        return left;
    }
};